The ultrasound probe has a plurality of piezoelectric bodies and an electrode to apply voltage between the piezoelectric bodies. There are various ways of deriving electricity from electrodes on the piezoelectric bodies. For example, there is a method of conductive the electrode with FPC (Flexible Printed Circuits), the electrode being arranged in front of the ultrasound radiation direction side of piezoelectric bodies. Signals derived from FPC are transmitted to a transmitter-receiver circuit.
Generally, the acoustic impedance of polyimides used as the base material of the FPC is approximately 3 Mrayl. Moreover, the acoustic impedance of piezoelectric bodies is 30 Mrayl or more. Due to such large differences, acoustic mismatching occurs when the FPC is directly connected to the piezoelectric bodies. When acoustic mismatching occurs, ultrasound beams are reflected in a boundary with great variance in acoustic impedance. One of methods to solve this is to provide an acoustic matching layer as an intermediate layer to efficiently propagate ultrasound waves between the FPC and the piezoelectric bodies.
Moreover, in order to reduce the acoustic mismatching mentioned above, a plurality of acoustic matching layers are sometimes configured. In said configuration, a plurality of acoustic matching layers are stacked in stages, the acoustic matching layers having different acoustic impedance between the acoustic impedance of FPC (for example, 3 Mrayl) and the acoustic impedance of piezoelectric bodies (for example, 30 Mrayl).
In said configuration, for example, if the acoustic impedance preferred for the first layer of the acoustic matching layers is approximately 9 to 15 Mrayl, a material having such acoustic impedance may be a machinable ceramic. Machinable ceramics are mainly composed of mica and are non- conductive.
Here, a configuration that electrically conducts from the electrodes of the piezoelectric bodies to FPC (conductive path) must be formed. Accordingly, when arranging the non-conductive acoustic matching layer on the first layer, the conductive path must be provided on said non-conductive acoustic matching layer.
For example, in a two-dimensional array ultrasound transducer, electrodes must be derived to the FPC from each of a huge number of elements. Therefore, conventionally, an ultrasound transducer configured with an open hole with electric conductivity is provided in correspondence with the number and arrangement of the piezoelectric bodies in the layering direction with respect to the non-conductive acoustic matching layer. In said ultrasound transducer, several open holes are provided on the acoustic matching layer and all surfaces of said open hole are, for example, plated in order to ensure the conductive path.
Moreover, there is conventionally a method of manufacturing the ultrasound transducer having: forming a board with the non-conductive material provided with a conductive film on both surfaces, and overlapping both surfaces of the conductive film of the board thereof to form the non-conductive acoustic matching layer. As an example, a board of the non-conductive material having the same width as the pitch of piezoelectric bodies is formed, and the conductive film is provided on both surfaces thereof. These boards are overlapped in a number corresponding to the number of columns or rows of the piezoelectric bodies to form several blocks, and to further overlap the blocks to form the acoustic matching layer. The acoustic matching layer formed by these processes allows the board and a overlapped surface of the board to function as the conductive path between the electrode and the FPC.